Grammarist is a professional online English grammar dictionary, that provides a variety of grammatical tools, rules and tips in order to improve your grammar and to help you distinguish between commonly misspelled words.

Vacuous vs. vapid

Someone or something that is vacuous is (1) devoid of matter, empty; or (2) lacking intelligence, inane. The conventional definition of vapid is lacking liveliness. It’s a synonym of dull. So to use vapid to insult someone’s intelligence is not in keeping with the traditional definition of the word. Vacuous would make more sense. Nevertheless, if you Google “vapid,” you’ll see that many people use it to mean stupid.